As the number of droughts increases globally, scientists are working to develop predictions of how future parched conditions will affect plants, especially trees. New results published today in the journal Nature Ecology and Evolution by 62 scientists, led by Henry Adams at Oklahoma State University, synthesized research from drought manipulation studies and revealed the mechanisms by which tree deaths happen.

“Understanding drought is critical to managing our nation’s forests,” says Lina Patino, a section head in the National Science Foundation’s (NSF) Division of Earth Sciences, which co-funded the study through its Critical Zone Observatories program. “This research will help us more accurately predict how trees will respond to environmental stresses, whether drought, insect damage or disease.”

Adds Liz Blood, director of NSF’s MacroSystems Biology program, which co-funded the research, “Droughts are simultaneously happening over large regions of the globe, affecting forests with very different trees. The discovery of how droughts cause mortality in trees, regardless of the type of tree, allows us to make better regional-scale predictions of droughts’ effects on forests.”

How trees respond to drought is important for models used to predict climate change. Plants take up a large portion of the carbon dioxide (CO2) in the atmosphere — fewer trees means more CO2. Sudden large-scale changes in plant populations, such as the tree die-offs observed worldwide in recent decades, could affect the rate at which climate changes.

Current global vegetation models have faced challenges in producing consistent estimates of plant CO2 uptake, scientists say. The predictions vary widely depending on assumptions about how plants respond to climate. One idea for improving the models is to base forest responses to climate change on how trees die in response to heat, drought and other stresses. But progress has been limited by disagreement over a central question: What, exactly, causes tree deaths?